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Geological natural hazards > Tsunami Hazards > Flashcards

Tsunami Hazards Flashcards

1
Q

What can tsunamis originate from?

A

Displacement of the water column by:
- Earthquakes
- Slope failure/ mass movements
- Volcanic activity
- Bolide impact

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2
Q

What do all tsunami sources have in common?

A

short lived water displacement disrupting the whole water body

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3
Q

What is the theory behind tsunamis?

A

Initial displacement - (water coloumn raised, gravitational spread of disturbance)

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4
Q

What is the period of a tsunami?

A

T - time for one wave to pass a point

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5
Q

How is tsunami velocity calculated?

A

Wavelength / time

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6
Q

What will the disturbance from tsunamis produce?

A

A wave-train of multiple waves

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7
Q

How will tsunami waves tend to behave? (particularly sesimogenic)

A

Shallow-water waves (due to the length to depth ratio)

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8
Q

What will the length of tsunamis typically be?

A

~200km

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9
Q

What will the typical period of a tsunami wave be?

A

10s of minutes

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10
Q

What will the amplitude of tsunami waves be in open ocean?

A

relativeky low (e.g 1m) compared to run up amplitude

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11
Q

How is the velocity for shallow water waves (tsunami) calculated?

A

sqaure root of gravity X depth

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12
Q

What is the energy loss if tsunami waves proportional to?

A

Wavelength - longer wavelengths more effieicnt so less energy loss leading to greater diatance travelled

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13
Q

What happens to tsunami waves when water gets shallower?

A

Velocity decreases but wave period stays constant so shorter wavelength and higher amplitude

Known as Shoaling or Amplification shorewards

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14
Q

Can wave speed by outrun on land?

A

Wave still approach rapidly at a speed too fast to outrun

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15
Q

What will the slope of a tsunami wave be like and how does this affect its appearance?

A

Still relatively gentle with wavelength of several km looks like a rapidly rising wave level instead of wall of water

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16
Q

How will the tsunami behave based on the displcement at fault?

A

Side which moved up will be peak followed by trough and side which moved down will be trough followed by peak

Thailand 04 water receded first but sri lanka had no warning

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17
Q

What was the ffect of the tsunami travelling across the indian ocean from sumatra 04?

A

Travelling through deeper ocean lead to increased wavelength

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18
Q

Wjat are the 5 main approaches of tsunami mitigation?

A
  1. Direct warning/ monitoring
  2. Planning - tsunami models
  3. Education and awareness
  4. Learning from past events
  5. Direct protection
19
Q

What was learnt for monitoring and warning post sumatra 2004?

A

Lack of Indian ocean wanring system (affetcing those whose didnt feel EQ)
Lack of public awarenss due to limited EQ activity/ tsunami in recent history

20
Q

What is an example of a real time monitoring system for tsunamis?

A

DART - direct detection and warning system

21
Q

Why are DART systems important?

A

Provide data to warn public
Accurate warning (minimise false alarms)
Direclty feed to real time models

But with time taken to recove data and then transmit to national and local scale wave might have alrady reached shore

22
Q

How does the DART system work?

A

Presseure sensor on the sea floor which communictes the passage of a tsunami to a buoy

Not affected by normal storm waves

23
Q

Where are DART systems usually placed?

A

On the oceanward side of faults to provide warning for areas with time to plan

24
Q

What is the assumed idea for people thinking to reach safety form tsunami locally?

A

Will feel EQ and head to higher ground

25
Q

What does effective tsunami mitigation rely on?

A

Alarm/ effective communication system
Local emergency plans (hazard map)
Evacuation routes
Public awareness

26
Q

What was the problem with detection of P and S waves from 04 by internaitonal seimsic netowkr?

A

By time waves had reaches australia and reort by usgs was published saying potential for tsunami shore was already inundated

27
Q

What was the main flaw of mitigation for 04 tsunami?

A

Aspects recognised but no confirmation of tsunami released

28
Q

What can be learnt from tsunami in 04?

A

Syeystms need to be in place on local scale
All potentially affectd countries net to be in network
Coordination of govenremnts
Improved sensor network

29
Q

How can tsunami planning via modelling be done?

A

Forecast parameters - rapid and accurate models with potential real time forecasts

30
Q

What are the 3 stages of tsunami modelling?

A

Wave generation
Tsunami propagation
Inundatrion

31
Q

Why is tsunami modelling done?

A

assesment of tsunami potential rely on data avaliable at the time with potential revision from monitoring data

32
Q

How is public awareness used to mitigate tsunamis?

A

Use of maps and signs key to directin potential responses

33
Q

Why is effective communication of tsunami process needed?

A

First wave not always largest (chile 1960 3rd was the biggest), potential for multiple waves over several hours

34
Q

What can be learnt from past tsunami events?

A

Where megathrusts occur
Recurrence time
If worst case scenario has been observed
Orphan tsunamis

35
Q

What is the problem with direct protection from tsunamis?

A

People might not be as preapred for evacuation due to faith in protection so can exacerbate the hazard
Based on worst case but what if wost case hasnt happened

36
Q

How can tsunamis be directly protected against?

A

Infrastructure - sea walls

37
Q

What was the effect of the fukishima nuclear power plant from tohoku 11?

A

Back up generators damaged leading to 3rd worst nuclear diaster - walls in place were 6 m but wave wave upto 13m

38
Q

What is thought to have exacerbated the tsunami height around northern japan?

A

Underwaterlandslides increased displacment

39
Q

What is the problem with non-siesmogenic tsunamis?

A

Not detectable so go unnoticed until wave arrives

40
Q

What will the characteristics of landslide induced tsunamis be like?

A

Still produce large local wave (size of displacing body)
Wave height might be larger than seismogenic but not as effcient so dissipate quickly

Locally high impact but with rapid decay

Some so big might still have potential to cross ocean basins

41
Q

How can volcanoes be tsunami sources?

A

Any submerged volcano or partially submerged or PDCs
Volcani landslides - extreme (volcanic islands)

42
Q

What type of tsunami was produed by Hunga Tonga?

A

Meteotsunami- air pressure disturbances

43
Q

Has the UK experinced tsunamis?

A

One ~8200 yrs ago from landsldie off norwegian continental shelf

44
Q

How can underwater topography affect tsunami proporgation?

A

If part of wave contacts shallower water causing slowing but wave behind is still moving fast through deeper water wave is ‘pushed’ in a new direction

Geological natural hazards (20 decks)

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